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In algebra, a primitive element of a co-algebra ''C'' (over an element ''g'') is an element ''x'' that satisfies : where is the co-multiplication and ''g'' is an element of ''C'' that maps to the multiplicative identity 1 of the base field under the co-unit (''g'' is called group-like). ''C'' is said to be primitively generated if it is generated by primitive elements. If ''C'' is a bi-algebra; i.e., a co-algebra that is also an algebra, then one usually takes ''g'' to be 1, the multiplicative identity of ''C''. If ''C'' is a bi-algebra, then the set of primitive elements form a Lie algebra with the usual commutator bracket (graded commutator if ''C'' is graded.) If ''A'' is a (certain graded) Hopf algebra over a field of characteristic zero, then the Milnor–Moore theorem states the universal enveloping algebra of the graded Lie algebra of primitive elements of ''A'' is isomorphic to ''A''. == References == *http://www.encyclopediaofmath.org/index.php/Primitive_element_in_a_co-algebra 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Primitive element (co-algebra)」の詳細全文を読む スポンサード リンク
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